Processes for increasing alcohol production

ABSTRACT

A process for reducing ethyl acetate and/or diethyl acetal concentration of a crude ethanol product by hydrolysis is disclosed. A portion of the water is initially separated from the crude ethanol product in a first column residue. Ethyl acetate in the first column distillate is hydrolyzed to form additional ethanol and acetic acid. Product ethanol is recovered in a second distillation column preferably in a side stream and acetic acid is removed in the second column residue.

FIELD OF THE INVENTION

The present invention relates generally to processes for producingalcohol and, in particular, to processes for increasing ethanolproduction by hydrolyzing ester contaminants contained in a crudeethanol product to form additional ethanol.

BACKGROUND OF THE INVENTION

Ethanol for industrial use is conventionally produced from petrochemicalfeed stocks, such as oil, natural gas, or coal, from feed stockintermediates, such as syngas, or from starchy materials or cellulosematerials, such as corn or sugar cane. Conventional methods forproducing ethanol from petrochemical feed stocks, as well as fromcellulose materials, include the acid-catalyzed hydration of ethylene,methanol homologation, direct alcohol synthesis, and Fischer-Tropschsynthesis. Instability in petrochemical feed stock prices contributes tofluctuations in the cost of conventionally produced ethanol, making theneed for alternative sources of ethanol production all the greater whenfeed stock prices rise. Starchy materials, as well as cellulosematerial, are converted to ethanol by fermentation. However,fermentation is typically used for consumer production of ethanol, whichis suitable for fuels or human consumption. In addition, fermentation ofstarchy or cellulose materials competes with food sources and placesrestraints on the amount of ethanol that can be produced for industrialuse.

Ethanol production via the reduction of alkanoic acids and/or othercarbonyl group-containing compounds has been widely studied, and avariety of combinations of catalysts, supports, and operating conditionshave been mentioned in the literature. During the reduction of alkanoicacid, e.g., acetic acid, other compounds are formed with ethanol or areformed in side reactions. These impurities limit the production andrecovery of ethanol from such reaction mixtures. For example, duringhydrogenation, esters are produced that together with ethanol and/orwater form azeotropes, which are difficult to separate. In addition whenconversion is incomplete, unreacted acetic acid remains in the crudeethanol product, which must be removed to recover ethanol.

EP02060553 describes a process for converting hydrocarbons to ethanolinvolving converting the hydrocarbons to ethanoic acid and hydrogenatingthe ethanoic acid to ethanol. The stream from the hydrogenation reactoris separated to obtain an ethanol stream and a stream of acetic acid andethyl acetate, which is recycled to the hydrogenation reactor.

The need remains for improved processes for recovering ethanol from acrude product obtained by reducing alkanoic acids, such as acetic acid,and/or other carbonyl group-containing compounds. In addition, the needexists for reducing the amount of impurities, such as ester impurities,that are formed as byproducts of the hydrogenation reaction.

SUMMARY OF THE INVENTION

The present invention is directed to improved processes for recoveringethanol and for improved processes for reducing the amount ofimpurities, in particular ethyl acetate, formed in an acetic acidhydrogenation process. In a first embodiment, the present invention isdirected to a process for producing ethanol, the process comprising thesteps of: (a) hydrogenating acetic acid in a reactor in the presence ofa catalyst to form a crude ethanol product; (b) separating at least aportion of the crude ethanol product in a first distillation column toyield a first distillate comprising ethanol and ethyl acetate and afirst residue comprising acetic acid; and (c) separating at least aportion of the first distillate in a second distillation column to yielda second distillate comprising ethyl acetate and a side streamcomprising ethanol. In one aspect, the process of the present inventionfurther comprises the step of hydrolyzing a portion of the ethyl acetatein the first distillate to form ethanol and acetic acid. Step (c) mayfurther comprise forming a second residue comprising acetic acid.

In a second embodiment, the present invention is directed to a processfor producing ethanol, the process comprising the steps of: (a)hydrogenating acetic acid in a reactor in the presence of a catalyst toform a crude ethanol product; (b) separating at least a portion of thecrude ethanol product in a first distillation column to yield a firstdistillate comprising ethanol and ethyl acetate and a first residuecomprising acetic acid; (c) hydrolyzing at least a portion of the ethylacetate under conditions effective to form additional ethanol andadditional acetic acid; and (d) separating at least a portion of thefirst distillate in a second distillation column to yield a side streamcomprising ethanol and a second residue comprising the residual aceticacid.

In a third embodiment, the present invention is directed to a processfor producing ethanol, the process comprising the steps of: (a)hydrogenating acetic acid in a reactor in the presence of a catalyst toform a crude ethanol product; (b) separating at least a portion of thecrude ethanol product in a first distillation column to yield a firstdistillate comprising ethanol, ethyl acetate and a minor amount ofacetic acid and a first residue comprising acetic acid; (c) increasingthe amount of ethanol and the amount of acetic acid in the firstdistillate; and (d) separating at least a portion of the firstdistillate in a second distillation column to yield a second distillatecomprising ethyl acetate and a side stream comprising ethanol. In oneaspect, step (d) further comprises forming a second residue comprisingacetic acid.

In a fourth embodiment, the present invention is directed to a processfor purifying a crude ethanol product comprising ethanol, ethyl acetateand acetic acid, the process comprising the steps of: (a) separating atleast a portion of the crude ethanol product in a first distillationcolumn to yield a first distillate comprising ethanol and ethyl acetateand a first residue comprising acetic acid; and (b) separating at leasta portion of the first distillate in a second distillation column toyield a second distillate comprising ethyl acetate, a side streamcomprising ethanol, and optionally a second residue comprising aceticacid. In one aspect, the process of the present invention furthercomprises hydrolyzing at least a portion of the ethyl acetate in thefirst distillate to form a hydrolyzed second distillate comprisingethanol and acetic acid prior to being separated in step (b).

BRIEF DESCRIPTION OF DRAWINGS

The invention may be more completely understood in consideration of thefollowing detailed description of various embodiments of the inventionin connection with the accompanying drawings, wherein like numeralsdesignate similar parts.

FIG. 1 is a schematic diagram of an ethanol production system with ahydrolysis unit and a water separator for removing water from the firstdistillate in accordance with one embodiment of the present invention.

FIG. 2 is a schematic diagram of an ethanol production system with ahydrolysis unit and a membrane for removing water from the firstdistillate in accordance with one embodiment of the present invention.

FIG. 3 is a schematic diagram of a water separator for removing waterfrom the first distillate in accordance with one embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

Introduction

The present invention relates to processes for recovering ethanol,optionally from a crude ethanol product produced by hydrogenating aceticacid in the presence of a catalyst. The crude ethanol product formed bythe hydrogenation reaction may comprise ethanol, water, ethyl acetate,unreacted acetic acid, and other impurities. The concentration of someof these compounds in the reaction mixture is largely a factor ofcatalyst composition and process conditions. However, waterconcentration in the reaction mixture is not dictated by these factorsbecause water is co-produced with ethanol in the hydrogenation reactionin about a 1:1 molar ratio. Thus, producing additional ethanol alsoresults in the production of additional water.

In addition to water, a crude ethanol product formed from thehydrogenation of acetic acid typically contains ethyl acetate (EtOAc),which is formed along with water from the equilibrium reaction betweenethanol (EtOH) and unreacted acetic acid (HOAc), as follows.HOAc+EtOH⇄EtOAc+H₂O

Diethyl acetal (DEA) also may be formed with water from ethanol andacetaldehyde (AcH) according to the following reaction.2EtOH+AcH⇄DEA+H₂O

The present invention advantageously reduces the amount of ethyl acetateand DEA in a crude ethanol product and provides a low energy separationscheme for recovering product ethanol. In a preferred embodiment, theprocess comprises the steps of: (a) hydrogenating acetic acid in areactor in the presence of a catalyst to form a crude ethanol product;(b) separating at least a portion of the crude ethanol product in afirst distillation column to yield a first distillate comprisingethanol, ethyl acetate and/or DEA and a first residue comprising aceticacid; and (c) separating at least a portion of the first distillate in asecond distillation column to yield a second distillate comprising ethylacetate, a side stream comprising ethanol and optionally a secondresidue comprising acetic acid and/or DEA. Preferably, the processfurther comprises the step of hydrolyzing a portion of the ethyl acetatein the first distillate to form ethanol and acetic acid therebyincreasing overall selectivity to ethanol. Additionally oralternatively, the process further comprises the step of hydrolyzing aportion of the DEA in the first distillate to form ethanol andacetaldehyde.

Hydrogenation of Acetic Acid

The process of the present invention may be used with any hydrogenationprocess for producing ethanol or with any other process that forms acrude ethanol product, as defined herein. The materials, catalysts,reaction conditions, and separation processes that may be used in thehydrogenation of acetic acid are described further below.

The raw materials, acetic acid and hydrogen, used in connection with theprocess of this invention may be derived from any suitable sourceincluding natural gas, petroleum, coal, biomass, and so forth. Asexamples, acetic acid may be produced via methanol carbonylation,acetaldehyde oxidation, ethylene oxidation, oxidative fermentation, andanaerobic fermentation. Methanol carbonylation processes suitable forproduction of acetic acid are described in U.S. Pat. Nos. 7,208,624;7,115,772; 7,005,541; 6,657,078; 6,627,770; 6,143,930; 5,599,976;5,144,068; 5,026,908; 5,001,259; and U.S. Pat. No. 4,994,608, the entiredisclosures of which are incorporated herein by reference. Optionally,the production of ethanol may be integrated with such methanolcarbonylation processes.

As petroleum and natural gas prices fluctuate becoming either more orless expensive, methods for producing acetic acid and intermediates suchas methanol and carbon monoxide from alternate carbon sources have drawnincreasing interest. In particular, when petroleum is relativelyexpensive, it may become advantageous to produce acetic acid fromsynthesis gas (“syngas”) that is derived from more available carbonsources. U.S. Pat. No. 6,232,352, the entirety of which is incorporatedherein by reference, for example, teaches a method of retrofitting amethanol plant for the manufacture of acetic acid. By retrofitting amethanol plant, the large capital costs associated with CO generationfor a new acetic acid plant are significantly reduced or largelyeliminated. All or part of the syngas is diverted from the methanolsynthesis loop and supplied to a separator unit to recover CO, which isthen used to produce acetic acid. In a similar manner, hydrogen for thehydrogenation step may be supplied from syngas.

In some embodiments, some or all of the raw materials for theabove-described acetic acid hydrogenation process may be derivedpartially or entirely from syngas. For example, the acetic acid may beformed from methanol and carbon monoxide, both of which may be derivedfrom syngas. The syngas may be formed by partial oxidation reforming orsteam reforming, and the carbon monoxide may be separated from syngas.Similarly, hydrogen that is used in the step of hydrogenating the aceticacid to form the crude ethanol product may be separated from syngas. Thesyngas, in turn, may be derived from variety of carbon sources. Thecarbon source, for example, may be selected from the group consisting ofnatural gas, oil, petroleum, coal, biomass, and combinations thereof.Syngas or hydrogen may also be obtained from bio-derived methane gas,such as bio-derived methane gas produced by landfills or agriculturalwaste.

In another embodiment, the acetic acid used in the hydrogenation stepmay be formed from the fermentation of biomass. The fermentation processpreferably utilizes an acetogenic process or a homoacetogenicmicroorganism to ferment sugars to acetic acid producing little, if any,carbon dioxide as a by-product. The carbon efficiency for thefermentation process preferably is greater than 70%, greater than 80% orgreater than 90% as compared to conventional yeast processing, whichtypically has a carbon efficiency of about 67%. Optionally, themicroorganism employed in the fermentation process is of a genusselected from the group consisting of Clostridium, Lactobacillus,Moorella, Thermoanaerobacter, Propionibacterium, Propionispera,Anaerobiospirillum, and Bacteriodes, and in particular, species selectedfrom the group consisting of Clostridium formicoaceticum, Clostridiumbutyricum, Moorella thermoacetica, Thermoanaerobacter kivui,Lactobacillus delbrukii, Propionibacterium acidipropionici,Propionispera arboris, Anaerobiospirillum succinicproducens, Bacteriodesamylophilus and Bacteriodes ruminicola. Optionally in this process, allor a portion of the unfermented residue from the biomass, e.g., lignans,may be gasified to form hydrogen that may be used in the hydrogenationstep of the present invention. Exemplary fermentation processes forforming acetic acid are disclosed in U.S. Pat. Nos. 6,509,180;6,927,048; 7,074,603; 7,507,562; 7,351,559; 7,601,865; 7,682,812; andU.S. Pat. No. 7,888,082, the entireties of which are incorporated hereinby reference. See also U.S. Pub. Nos. 2008/0193989 and 2009/0281354, theentireties of which are incorporated herein by reference.

Examples of biomass include, but are not limited to, agriculturalwastes, forest products, grasses, and other cellulosic material, timberharvesting residues, softwood chips, hardwood chips, tree branches, treestumps, leaves, bark, sawdust, off-spec paper pulp, corn, corn stover,wheat straw, rice straw, sugarcane bagasse, switchgrass, miscanthus,animal manure, municipal garbage, municipal sewage, commercial waste,grape pumice, almond shells, pecan shells, coconut shells, coffeegrounds, grass pellets, hay pellets, wood pellets, cardboard, paper,plastic, and cloth. See, e.g., U.S. Pat. No. 7,884,253, the entirety ofwhich is incorporated herein by reference. Another biomass source isblack liquor, a thick, dark liquid that is a byproduct of the Kraftprocess for transforming wood into pulp, which is then dried to makepaper. Black liquor is an aqueous solution of lignin residues,hemicellulose, and inorganic chemicals.

U.S. Pat. No. RE 35,377, also incorporated herein by reference, providesa method for the production of methanol by conversion of carbonaceousmaterials such as oil, coal, natural gas and biomass materials. Theprocess includes hydrogasification of solid and/or liquid carbonaceousmaterials to obtain a process gas which is steam pyrolized withadditional natural gas to form synthesis gas. The syngas is converted tomethanol which may be carbonylated to acetic acid. The method likewiseproduces hydrogen which may be used in connection with this invention asnoted above. U.S. Pat. No. 5,821,111, which discloses a process forconverting waste biomass through gasification into synthesis gas, andU.S. Pat. No. 6,685,754, which discloses a method for the production ofa hydrogen-containing gas composition, such as a synthesis gas includinghydrogen and carbon monoxide, are incorporated herein by reference intheir entireties.

The acetic acid fed to the hydrogenation reaction may also compriseother carboxylic acids and anhydrides, as well as acetaldehyde andacetone. Preferably, a suitable acetic acid feed stream comprises one ormore of the compounds selected from the group consisting of acetic acid,acetic anhydride, acetaldehyde, ethyl acetate, and mixtures thereof.These other compounds may also be hydrogenated in the processes of thepresent invention. In some embodiments, the presence of carboxylicacids, such as propanoic acid or its anhydride, may be beneficial inproducing propanol. Water may also be present in the acetic acid feed.

Alternatively, acetic acid in vapor form may be taken directly as crudeproduct from the flash vessel of a methanol carbonylation unit of theclass described in U.S. Pat. No. 6,657,078, the entirety of which isincorporated herein by reference. The crude vapor product, for example,may be fed directly to the ethanol synthesis reaction zones of thepresent invention without the need for condensing the acetic acid andlight ends or removing water, saving overall processing costs.

The acetic acid may be vaporized at the reaction temperature, followingwhich the vaporized acetic acid may be fed along with hydrogen in anundiluted state or diluted with a relatively inert carrier gas, such asnitrogen, argon, helium, carbon dioxide and the like. For reactions runin the vapor phase, the temperature should be controlled in the systemsuch that it does not fall below the dew point of acetic acid. In oneembodiment, the acetic acid may be vaporized at the boiling point ofacetic acid at the particular pressure, and then the vaporized aceticacid may be further heated to the reactor inlet temperature. In anotherembodiment, the acetic acid is mixed with other gases before vaporizing,followed by heating the mixed vapors up to the reactor inlettemperature. Preferably, the acetic acid is transferred to the vaporstate by passing hydrogen and/or recycle gas through the acetic acid ata temperature at or below 125° C., followed by heating of the combinedgaseous stream to the reactor inlet temperature.

Some embodiments of the process of hydrogenating acetic acid to formethanol may include a variety of configurations using a fixed bedreactor or a fluidized bed reactor. In many embodiments of the presentinvention, an “adiabatic” reactor can be used; that is, there is littleor no need for internal plumbing through the reaction zone to add orremove heat. In other embodiments, a radial flow reactor or reactors maybe employed, or a series of reactors may be employed with or withoutheat exchange, quenching, or introduction of additional feed material.Alternatively, a shell and tube reactor provided with a heat transfermedium may be used. In many cases, the reaction zone may be housed in asingle vessel or in a series of vessels with heat exchangerstherebetween.

In preferred embodiments, the catalyst is employed in a fixed bedreactor, e.g., in the shape of a pipe or tube, where the reactants,typically in the vapor form, are passed over or through the catalyst.Other reactors, such as fluid or ebullient bed reactors, can beemployed. In some instances, the hydrogenation catalysts may be used inconjunction with an inert material to regulate the pressure drop of thereactant stream through the catalyst bed and the contact time of thereactant compounds with the catalyst particles.

The hydrogenation reaction may be carried out in either the liquid phaseor vapor phase. Preferably, the reaction is carried out in the vaporphase under the following conditions. The reaction temperature may rangefrom 125° C. to 350° C., e.g., from 200° C. to 325° C., from 225° C. to300° C., or from 250° C. to 300° C. The pressure may range from 10 kPato 3000 kPa, e.g., from 50 kPa to 2300 kPa, or from 100 kPa to 1500 kPa.The reactants may be fed to the reactor at a gas hourly space velocity(GHSV) of greater than 500 hr⁻¹, e.g., greater than 1000 hr⁻¹, greaterthan 2500 hr⁻¹ or even greater than 5000 hr⁻¹. In terms of ranges theGHSV may range from 50 hr⁻¹ to 50,000 hr⁻¹, e.g., from 500 hr⁻¹ to30,000 hr⁻¹, from 1000 hr⁻¹ to 10,000 hr⁻¹, or from 1000 hr⁻¹ to 6500hr⁻¹.

The hydrogenation optionally is carried out at a pressure justsufficient to overcome the pressure drop across the catalytic bed at theGHSV selected, although there is no bar to the use of higher pressures,it being understood that considerable pressure drop through the reactorbed may be experienced at high space velocities, e.g., 5000 hr⁻¹ or6,500 hr⁻¹.

Although the reaction consumes two moles of hydrogen per mole of aceticacid to produce one mole of ethanol, the actual molar ratio of hydrogento acetic acid in the feed stream may vary from about 100:1 to 1:100,e.g., from 50:1 to 1:50, from 20:1 to 1:2, or from 12:1 to 1:1. Mostpreferably, the molar ratio of hydrogen to acetic acid is greater than2:1, e.g., greater than 4:1 or greater than 8:1.

Contact or residence time can also vary widely, depending upon suchvariables as amount of acetic acid, catalyst, reactor, temperature, andpressure. Typical contact times range from a fraction of a second tomore than several hours when a catalyst system other than a fixed bed isused, with preferred contact times, at least for vapor phase reactions,of from 0.1 to 100 seconds, e.g., from 0.3 to 80 seconds or from 0.4 to30 seconds.

The hydrogenation of acetic acid to form ethanol is preferably conductedin the presence of a hydrogenation catalyst. Suitable hydrogenationcatalysts include catalysts comprising a first metal and optionally oneor more of a second metal, a third metal or any number of additionalmetals, optionally on a catalyst support. The first and optional secondand third metals may be selected from Group IB, IIB, IIIB, IVB, VB,VIIB, VIIB, VIII transition metals, a lanthanide metal, an actinidemetal or a metal selected from any of Groups IIIA, IVA, VA, and VIA.Preferred metal combinations for some exemplary catalyst compositionsinclude platinum/tin, platinum/ruthenium, platinum/rhenium,palladium/ruthenium, palladium/rhenium, cobalt/palladium,cobalt/platinum, cobalt/chromium, cobalt/ruthenium, cobalt/tin,silver/palladium, copper/palladium, copper/zinc, nickel/palladium,gold/palladium, ruthenium/rhenium, and ruthenium/iron. Exemplarycatalysts are further described in U.S. Pat. No. 7,608,744 and U.S. Pub.No. 2010/0029995, the entireties of which are incorporated herein byreference. In another embodiment, the catalyst comprises a Co/Mo/Scatalyst of the type described in U.S. Pub. No. 2009/0069609, theentirety of which is incorporated herein by reference.

In one embodiment, the catalyst comprises a first metal selected fromthe group consisting of copper, iron, cobalt, nickel, ruthenium,rhodium, palladium, osmium, iridium, platinum, titanium, zinc, chromium,rhenium, molybdenum, and tungsten. Preferably, the first metal isselected from the group consisting of platinum, palladium, cobalt,nickel, and ruthenium. More preferably, the first metal is selected fromplatinum and palladium. In embodiments of the invention where the firstmetal comprises platinum, it is preferred that the catalyst comprisesplatinum in an amount less than 5 wt. %, e.g., less than 3 wt. % or lessthan 1 wt. %, due to the high commercial demand for platinum.

As indicated above, in some embodiments, the catalyst further comprisesa second metal, which typically would function as a promoter. Ifpresent, the second metal preferably is selected from the groupconsisting of copper, molybdenum, tin, chromium, iron, cobalt, vanadium,tungsten, palladium, platinum, lanthanum, cerium, manganese, ruthenium,rhenium, gold, and nickel. More preferably, the second metal is selectedfrom the group consisting of copper, tin, cobalt, rhenium, and nickel.More preferably, the second metal is selected from tin and rhenium.

In certain embodiments where the catalyst includes two or more metals,e.g., a first metal and a second metal, the first metal is present inthe catalyst in an amount from 0.1 to 10 wt. %, e.g., from 0.1 to 5 wt.%, or from 0.1 to 3 wt. %. The second metal preferably is present in anamount from 0.1 to 20 wt. %, e.g., from 0.1 to 10 wt. %, or from 0.1 to5 wt. %. For catalysts comprising two or more metals, the two or moremetals may be alloyed with one another or may comprise a non-alloyedmetal solution or mixture.

The preferred metal ratios may vary depending on the metals used in thecatalyst. In some exemplary embodiments, the mole ratio of the firstmetal to the second metal is from 10:1 to 1:10, e.g., from 4:1 to 1:4,from 2:1 to 1:2, from 1.5:1 to 1:1.5 or from 1.1:1 to 1:1.1.

The catalyst may also comprise a third metal selected from any of themetals listed above in connection with the first or second metal, solong as the third metal is different from the first and second metals.In preferred aspects, the third metal is selected from the groupconsisting of cobalt, palladium, ruthenium, copper, zinc, platinum, tin,and rhenium. More preferably, the third metal is selected from cobalt,palladium, and ruthenium. When present, the total weight of the thirdmetal preferably is from 0.05 to 4 wt. %, e.g., from 0.1 to 3 wt. %, orfrom 0.1 to 2 wt. %.

In addition to one or more metals, in some embodiments of the presentinvention the catalysts further comprise a support or a modifiedsupport. As used herein, the term “modified support” refers to a supportthat includes a support material and a support modifier, which adjuststhe acidity of the support material.

The total weight of the support or modified support, based on the totalweight of the catalyst, preferably is from 75 to 99.9 wt. %, e.g., from78 to 97 wt. %, or from 80 to 95 wt. %. In preferred embodiments thatutilize a modified support, the support modifier is present in an amountfrom 0.1 to 50 wt. %, e.g., from 0.2 to 25 wt. %, from 0.5 to 15 wt. %,or from 1 to 8 wt. %, based on the total weight of the catalyst. Themetals of the catalysts may be dispersed throughout the support, layeredthroughout the support, coated on the outer surface of the support(i.e., egg shell), or decorated on the surface of the support.

As will be appreciated by those of ordinary skill in the art, supportmaterials are selected such that the catalyst system is suitably active,selective and robust under the process conditions employed for theformation of ethanol.

Suitable support materials may include, for example, stable metaloxide-based supports or ceramic-based supports. Preferred supportsinclude silicaceous supports, such as silica, silica/alumina, a GroupIIA silicate such as calcium metasilicate, pyrogenic silica, high puritysilica, and mixtures thereof. Other supports may include, but are notlimited to, iron oxide, alumina, titania, zirconia, magnesium oxide,carbon, graphite, high surface area graphitized carbon, activatedcarbons, and mixtures thereof.

As indicated, the catalyst support may be modified with a supportmodifier. In some embodiments, the support modifier may be an acidicmodifier that increases the acidity of the catalyst. Suitable acidicsupport modifiers may be selected from the group consisting of: oxidesof Group IVB metals, oxides of Group VB metals, oxides of Group VIBmetals, oxides of Group VIIB metals, oxides of Group VIIIB metals,aluminum oxides, and mixtures thereof. Acidic support modifiers includethose selected from the group consisting of TiO₂, ZrO₂, Nb₂O₅, Ta₂O₅,Al₂O₃, B₂O₃, P₂O₅, and Sb₂O₃. Preferred acidic support modifiers includethose selected from the group consisting of TiO₂, ZrO₂, Nb₂O₅, Ta₂O₅,and Al₂O₃. The acidic modifier may also include WO₃, MoO₃, Fe₂O₃, Cr₂O₃,V₂O₅, MnO₂, CuO, Co₂O₃, and Bi₂O₃.

In another embodiment, the support modifier may be a basic modifier thathas a low volatility or no volatility. Such basic modifiers, forexample, may be selected from the group consisting of: (i) alkalineearth oxides, (ii) alkali metal oxides, (iii) alkaline earth metalmetasilicates, (iv) alkali metal metasilicates, (v) Group IIB metaloxides, (vi) Group IIB metal metasilicates, (vii) Group IIIB metaloxides, (viii) Group IIIB metal metasilicates, and mixtures thereof. Inaddition to oxides and metasilicates, other types of modifiers includingnitrates, nitrites, acetates, and lactates may be used. Preferably, thesupport modifier is selected from the group consisting of oxides andmetasilicates of any of sodium, potassium, magnesium, calcium, scandium,yttrium, and zinc, as well as mixtures of any of the foregoing. Morepreferably, the basic support modifier is a calcium silicate, and evenmore preferably calcium metasilicate (CaSiO₃). If the basic supportmodifier comprises calcium metasilicate, it is preferred that at least aportion of the calcium metasilicate is in crystalline form.

A preferred silica support material is SS61138 High Surface Area (HSA)Silica Catalyst Carrier from Saint Gobain N or Pro. The Saint-Gobain Nor Pro SS61138 silica exhibits the following properties: containsapproximately 95 wt. % high surface area silica; surface area of about250 m²/g; median pore diameter of about 12 nm; average pore volume ofabout 1.0 cm³/g as measured by mercury intrusion porosimetry and apacking density of about 0.352 g/cm³ (22 lb/ft³).

A preferred silica/alumina support material is KA-160 silica spheresfrom Sud Chemie having a nominal diameter of about 5 mm, a density ofabout 0.562 g/ml, an absorptivity of about 0.583 g H₂O/g support, asurface area of about 160 to 175 m²/g, and a pore volume of about 0.68ml/g.

The catalyst compositions suitable for use with the present inventionpreferably are formed through metal impregnation of the modifiedsupport, although other processes such as chemical vapor deposition mayalso be employed. Such impregnation techniques are described in U.S.Pat. No. 7,608,744 and U.S. Pat. No. 7,863,489 and U.S. Pub. No.2010/0197485 referred to above, the entireties of which are incorporatedherein by reference.

In particular, the hydrogenation of acetic acid may achieve favorableconversion of acetic acid and favorable selectivity and productivity toethanol. For purposes of the present invention, the term “conversion”refers to the amount of acetic acid in the feed that is converted to acompound other than acetic acid. Conversion is expressed as a molepercentage based on acetic acid in the feed. The conversion may be atleast 10%, e.g., at least 20%, at least 40%, at least 50%, at least 60%,at least 70% or at least 80%. Although catalysts that have highconversions are desirable, such as at least 80% or at least 90%, in someembodiments a low conversion may be acceptable at high selectivity forethanol. It is, of course, well understood that in many cases, it ispossible to compensate for conversion by appropriate recycle streams oruse of larger reactors, but it is more difficult to compensate for poorselectivity.

Selectivity is expressed as a mole percent based on converted aceticacid. It should be understood that each compound converted from aceticacid has an independent selectivity and that selectivity is independentfrom conversion. For example, if 60 mole % of the converted acetic acidis converted to ethanol, we refer to the ethanol selectivity as 60%.Preferably, the catalyst selectivity to ethoxylates is at least 60%,e.g., at least 70%, or at least 80%. As used herein, the term“ethoxylates” refers specifically to the compounds ethanol,acetaldehyde, and ethyl acetate. Preferably, the selectivity to ethanolis at least 80%, e.g., at least 85% or at least 88%. Preferredembodiments of the hydrogenation process also have low selectivity toundesirable products, such as methane, ethane, and carbon dioxide. Theselectivity to these undesirable products preferably is less than 4%,e.g., less than 2% or less than 1%. More preferably, these undesirableproducts are present in undetectable amounts. Formation of alkanes maybe low, and ideally less than 2%, less than 1%, or less than 0.5% of theacetic acid passed over the catalyst is converted to alkanes, which havelittle value other than as fuel.

The term “productivity,” as used herein, refers to the grams of aspecified product, e.g., ethanol, formed during the hydrogenation basedon the kilograms of catalyst used per hour. A productivity of at least100 grams of ethanol per kilogram of catalyst per hour, e.g., at least400 grams of ethanol per kilogram of catalyst per hour or at least 600grams of ethanol per kilogram of catalyst per hour, is preferred. Interms of ranges, the productivity preferably is from 100 to 3,000 gramsof ethanol per kilogram of catalyst per hour, e.g., from 400 to 2,500grams of ethanol per kilogram of catalyst per hour or from 600 to 2,000grams of ethanol per kilogram of catalyst per hour.

Operating under the conditions of the present invention may result inethanol production on the order of at least 0.1 tons of ethanol perhour, e.g., at least 1 ton of ethanol per hour, at least 5 tons ofethanol per hour, or at least 10 tons of ethanol per hour. Larger scaleindustrial production of ethanol, depending on the scale, generallyshould be at least 1 ton of ethanol per hour, e.g., at least 15 tons ofethanol per hour or at least 30 tons of ethanol per hour. In terms ofranges, for large scale industrial production of ethanol, the process ofthe present invention may produce from 0.1 to 160 tons of ethanol perhour, e.g., from 15 to 160 tons of ethanol per hour or from 30 to 80tons of ethanol per hour. Ethanol production from fermentation, due theeconomies of scale, typically does not permit the single facilityethanol production that may be achievable by employing embodiments ofthe present invention.

In various embodiments of the present invention, the crude ethanolproduct produced by the hydrogenation process, before any subsequentprocessing, such as purification and separation, will typically compriseunreacted acetic acid, ethanol and water. As used herein, the term“crude ethanol product” refers to any composition comprising from 5 to70 wt. % ethanol and from 5 to 40 wt. % water. Exemplary compositionalranges for the crude ethanol product are provided in Table 1. The“others” identified in Table 1 may include, for example, esters, ethers,aldehydes, ketones, alkanes, and carbon dioxide.

TABLE 1 CRUDE ETHANOL PRODUCT COMPOSITIONS Conc. Conc. Conc. Conc.Component (wt. %) (wt. %) (wt. %) (wt. %) Ethanol 5 to 70 15 to 70  15to 50 25 to 50 Acetic Acid <90 0 to 50 15 to 70 20 to 70 Water 5 to 40 5to 30 10 to 30 10 to 26 Ethyl Acetate <30 <20  1 to 12  3 to 10Acetaldehyde <10  <3 0.1 to 3  0.2 to 2  Others 0.1 to 10  0.1 to 6  0.1 to 4  —

The amounts indicated as less than (<) in the tables throughout presentspecification are preferably not present and if present may be presentin trace amounts or in amounts greater than 0.0001 wt. % up to thespecified upper range limit.

In one embodiment, the crude ethanol product may comprise acetic acid inan amount less than 20 wt. %, e.g., of less than 15 wt. %, less than 10wt. % or less than 5 wt. %. In embodiments having lower amounts ofacetic acid, the conversion of acetic acid is preferably greater than75%, e.g., greater than 85% or greater than 90%. In addition, theselectivity to ethanol may also be preferably high, for example, greaterthan 75%, e.g., greater than 85% or greater than 90%.

Hydrolysis and Ethanol Recovery

The ethanol recovery process begins with the introduction of the crudeethanol product into an initial separation column (first column), whichseparates the crude ethanol product into a distillate comprisingethanol, ethyl acetate, optionally DEA and water, and a residuecomprising water and unreacted acetic acid. Preferably, a majority ofthe water from the crude ethanol product is separated into the residueof the first column (first residue), the conditions in the first columnare such that a sufficient amount of water enters the first distillatefor hydrolysis of the ethyl acetate and/or DEA. The amount of water inthe first distillate preferably is provided in excess relative to theamount of ethyl acetate in the first distillate. In some preferredembodiments, the first distillate has a water:ethyl acetate molar ratioof greater than 1:1, greater than 2:1, greater than 3:1, greater than5:1 or greater than 10:1. In some embodiments, additional water fromwithin or outside of the reaction system may be added to the firstdistillate to provide the desired water:ethyl acetate ratio.

In theoretical embodiments where ethanol and water are the only productsof the hydrogenation reaction, the crude ethanol product comprises 71.9wt. % ethanol and 28.1 wt. % water. However, not all of the acetic acidfed to the hydrogenation reactor is typically converted to ethanol.Subsequent reactions of ethanol, such as esterification, may form otherbyproducts such as ethyl acetate. Hence, ethyl acetate is a byproductthat reduces the yield of ethanol of the process and increases the wastethat must be taken out of the system. In accordance with a preferredembodiment of the invention, the distillate from the first column (firstdistillate) is directed, in whole or in part, to a hydrolysis unit inwhich ethyl acetate (and/or DEA) contained therein is hydrolyzed to formethanol and acetic acid or ethanol and acetaldehyde, respectively.

The esterification reaction that produces ethyl acetate has a liquidphase equilibrium constant (K_(est)) equal to 4.0. (See, for example,Witzeman and Agreda in, “Acetic Acid and its Derivatives,” MarcelDekker, NY, 1992, p. 271, the entirety of which is incorporated hereinby reference.) The hydrolysis of ethyl acetate has an equilibriumconstant, K_(hyd), of 0.25, which is the reciprocal of the K_(est).

${\begin{matrix}{{esterification},k_{1}} \\\left. {{EtOAc} + {H_{2}O}}\leftrightarrows{{HOAc} + {EtOH}} \right. \\{{hydrolysis},k_{2}}\end{matrix}\mspace{31mu} K_{hyd}} = {\frac{\lbrack{HOAc}\rbrack\lbrack{EtOH}\rbrack}{\lbrack{EtOAc}\rbrack\left\lbrack {H_{2}O} \right\rbrack} = 0.25}$

Until the excess acetic acid, which is not converted to products in thehydrogenation reactor, is substantially removed from the crude ethanolproduct, e.g., in an acid separation column, the composition favorsesterification of ethanol with acetic acid to form ethyl acetate andwater. In one embodiment of the present invention, substantially all ofthe excess acetic acid is removed. One or more derivative streams thatare formed in the separation system may contain small amounts of aceticacid. As such, any mixture of ethanol, ethyl acetate and water in thederivative streams are not at chemical equilibrium, and the hydrolysisof ethyl acetate is thermodynamically favored.

In one embodiment, as discussed above, ethyl acetate (and/or DEA) in thefirst distillate is hydrolyzed to reduce the concentration thereof andform additional ethanol and acetic acid (or ethanol and acetaldehyde).The first distillate preferably comprises ethanol, ethyl acetate andwater, wherein the water is present in an amount effective to hydrolyzethe ethyl acetate. Optionally, additional water may be added to thefirst distillate as necessary to provide the desired water:ethyl acetateratio. In addition, the first distillate preferably comprisessubstantially no acetic acid, e.g., less than 1 wt. % or less than 0.5wt %, although it is contemplated that in some embodiments, it may bedesirable to operate at increased water concentrations in the firstdistillate. Allowing more water to enter the first distillate results inincreasing acetic acid carry over into the first distillate due to thedifficulty in separating water from acetic acid. In any event, the firstdistillate preferably comprises no more than 3 wt. % acetic acid, or nomore than 2 wt. % acetic acid.

Although ethyl acetate may be hydrolyzed in the absence of a catalyst,it is a preferred that a catalyst is employed to increase reaction rate.The hydrolysis of the ethyl acetate may be performed under liquid phaseor gas phase conditions. In one embodiment, the hydrolysis of the ethylacetate is performed continuously under liquid phase conditions.

According to one embodiment of the invention, the first distillate ispassed through a hydrolysis unit comprising an ion exchange resinreactor bed. The ion exchange resin reactor bed may comprise a stronglyacidic heterogeneous or homogenous catalyst, such as for example a Lewisacid, strongly acidic ion exchange catalyst, inorganic acids, andmethanesulfonic acid. Exemplary catalysts include Amberlyst™ 15 (Rohmand Haas Company, Philadelphia, U.S.A.), Amberlyst™ 70, Dowex-M-31 (DowChemical Company), Dowex Monosphere M-31 (Dow Chemical Company), andPurolite CT type Catalysts (Purolite International SRL). The ionexchange resin reactor bed preferably is a gel or marco-reticular bed.Ion exchange resin reactor beds may be located externally to thedistillation columns or within a distillation column. The outflow of theion exchange resin reactor bed may be directly or indirectly returned tothe separation system, preferably to a water removal unit or a secondcolumn, as discussed below. The hydrolysis step may occur in the liquidphase or in the vapor phase.

In one embodiment, the hydrolysis unit is included within the firstcolumn, while in other embodiments, the hydrolysis unit may be separatefrom the first column. Thus, the first column may comprise a hydrolyzingsection, preferably in the upper portion of the first column or near thetop of the first column. The hydrolyzing section may comprise aninternal ion exchange resin reactor bed. In another embodiment, thehydrolyzing section is an enlarged portion of the first column, i.e.,has a greater cross-sectional diameter than the lower half of the firstcolumn. This configuration may increase the residence time of the lightboiling point materials in the column to facilitate further hydrolysisof ethyl acetate.

In one embodiment of the invention, other compounds may also behydrolyzed with the ethyl acetate, such as diethyl acetal (DEA).

After the hydrolysis step, water is then optionally removed from theresulting stream to form an ethanol mixture stream, preferablycomprising less than 10 wt. % water, less than 6 wt. % water or lessthan 4 wt. % water. In terms of ranges, the ethanol mixture stream maycomprise from 0.001 to 10 wt. % water, e.g., from 0.01 to 6 wt. % wateror from 0.1 to 4 wt. % water. Product ethanol is then recovered from theethanol mixture stream.

The water removal step should be carefully selected since water andethanol form an azeotrope that is difficult to separate in adistillation column. The ethanol-water azeotrope limits the recoverableethanol in conventional distillation columns to an ethanol productcomprising about 92-96 wt. % of ethanol. The energy required to approachthis azeotrope in a distillation column, regardless of the presence ofother compounds, is significant. The present invention involves usingless energy in the first column than would be required to approach theazeotrope, resulting in some water being carried overhead in the firstdistillate. After hydrolyzing the ethyl acetate and/or DEA, residualwater contained in the first distillate then may be removed from thedistillate using a water separator, which beneficially requires lessenergy than is required for approaching the water/ethanol azeotrope in adistillation column. Thus, the present invention provides a low energyapproach for (i) reducing ethyl acetate and/or DEA concentration in thefirst distillate, (ii) increasing overall ethanol selectivity, and (iii)dehydrating a crude ethanol product and thus removing water that isco-produced with ethanol.

The concentration of water in the first distillate after the hydrolysisstep may vary depending on the acetic acid conversion and the amount ofethyl acetate contained in the first distillate prior to the hydrolysisstep. In one embodiment, the first distillate comprises water in anamount greater than the amount of water in the ethanol/water azeotrope,e.g., in an amount greater than 4 wt. %, greater than 5 wt. %, orgreater than 7 wt. %. In terms of ranges, the first distillateoptionally comprises water in an amount from 4 wt. % to 38 wt. %, e.g.,from 7 wt. % to 32 wt. %, or from 7 wt. % to 25 wt. %. As discussedabove, the water preferably is present in an amount sufficient tohydrolyze the ethyl acetate and/or DEA contained in the firstdistillate, and preferably is present in the first distillate in anamount sufficient to provide a water:ethyl acetate molar ratio ofgreater than 1:1, greater than 2:1, greater than 3:1, greater than 5:1or greater than 10:1.

Because the water concentration in the first distillate is typicallygreater than the acceptable amount of water for industrial or fuel gradeethanol applications, in one embodiment of the present invention, theprocess involves removing a substantial portion of the water from thefirst distillate, preferably after the hydrolysis step, to produce anethanol mixture. Preferably, the water is removed before separating anyappreciable amount of organics, e.g., acetaldehyde. In one embodiment,the water is removed prior to condensing the first distillate. Forexample, the first distillate in the vapor phase may be fed to anadsorption unit comprising a molecular sieve or a membrane. In someembodiments, the first distillate is condensed to a liquid and fed to amembrane. The heat of vaporization for water is provided to the firstdistillate to allow water to permeate through the membrane. In preferredembodiments, at least 50% of the water in the first distillate isremoved, e.g., at least 60% of the water or at least 75% of the water,based on the total amount of water in the first distillate. In morepreferred embodiments, from 90 to 99% of the water may be removed fromthe first distillate. Thus, the resulting ethanol mixture may compriseonly a minor amount of water, from 0.01 to 10 wt. %, e.g., from 0.5 to 6wt. %, or from 0.5 to 4 wt. %. In addition, since the ethyl acetate hasbeen hydrolyzed, the resulting ethanol mixture also preferably comprisesonly a minor amount of ethyl acetate, e.g., from 0.1 to 50 wt. %, from0.5 to 25 wt. % or from 1 to 15 wt. %. If the ethanol mixture containsDEA, it preferably comprises only a lower amount of DEA, e.g., from 10wppm to 10000 wppm, from 25 to 5000 wppm or from 50 to 1500 wppm. In oneembodiment, the ethanol mixture comprises a water concentration that isless than the amount of water in the ethanol/water azeotrope. In orderto achieve a water concentration that is below the amount of water inthe ethanol/water azeotrope, a large of amount of energy is required.Thus, the present invention beneficially removes water from the firstdistillate, after the hydrolysis step, to yield an ethanol mixturewithout using a large amount of energy. Also, because the ethanolmixture comprises less water, the need to remove water during laterstages of product separation is also reduced.

The process of the present invention may use any suitable technique forremoving water from the first distillate after the hydrolysis step. Forexample, water may be removed in the vapor phase, before condensation,or in the liquid phase. Water may be removed, for example, using anadsorption unit, membrane, molecular sieves, extractive columndistillation, or a combination thereof. Suitable adsorption unitsinclude pressure swing adsorption (PSA) units and thermal swingadsorption (TSA) units. The adsorption units may comprises molecularsieves, such as aluminosilicate compounds.

A membrane or an array of membranes may also be employed to separatewater from the distillate. The membrane or array of membranes may beselected from any suitable membrane that is capable of removing apermeate water stream from a stream that also comprises ethanol andethyl acetate.

In an exemplary embodiment, the energy requirements of the first columnin the process according to the present invention may be less than 5.5MMBtu per ton of refined ethanol, e.g., less than 4.5 MMBtu per ton ofrefined ethanol or less than 3.5 MMBtu per ton of refined ethanol. Insome embodiments, the process may operate with higher energyrequirements provided that the total energy requirement is less than theenergy required to remove most of the water from the crude ethanolproduct in the distillate, e.g., more than 65% of the water in the crudeethanol product.

The water that is removed from the first distillate after the hydrolysisstep may be returned to the first column and ultimately removed from thefirst column via the first residue. In one embodiment, a portion of theremoved water may be condensed and returned below the feed point of thecrude ethanol product to the first column, e.g., near the bottom of thefirst column. Depending on the water removal technique, there may besome ethanol and ethyl acetate in the removed water and thus it may bedesirable to recover these compounds by returning at least a portion ofthe removed water to the first column. Returning the removed water tothe first column may increase the amount of water withdrawn as theresidue. In other embodiments, a portion of the removed water may be fedto a separation column, e.g., a second column, preferably a secondcolumn, used in recovering an ethanol product from the ethanol mixture.The presence of a small amount of water, e.g., less than 10 wt. % waterbased on the total feed, in the second column may be beneficial infacilitating the separation of ethanol from other components, e.g.,acetic acid (which may be made up of unreacted acetic acid and/or aceticacid formed from the hydrolysis of ethyl acetate), residual ethylacetate or acetaldehyde, that may be present in the ethanol mixture. Aportion of the removed water may also be purged as needed to removewater from the system.

In a preferred embodiment, the second column separates the ethanolproduct in a side stream, and removes acetic acid formed in thehydrolysis step via the residue (the second residue). In someembodiments, the ratio of ethanol separated in the side stream toethanol separated in the second residue is from 100:1 to 1:10, e.g.,from 50:1 to 1:5 or from 20:1 to 1:2. Any residual ethyl acetate and/oracetaldehyde (e.g., formed from the hydrolysis of DEA), may be removedin a second distillate of the second column.

The ethanol mixture that is formed after hydrolysis and preferably afterthe water removal step may enter the second column above or below wherethe product ethanol side stream exits the column. Feeding the ethanolmixture into the second column above the side stream, may result inacetic acid going into the ethanol product (side stream). Conversely,adding the ethanol mixture to the second column below the side streammay result in unreacted ethyl acetate going into the ethanol product.

All or a portion of the second distillate may be sent to the reactor orreaction zone for conversion thereof to additional ethanol. Similarly,all or a portion of the second residue, particularly the acetic acid inthe second residue, may be sent to the reactor or reaction zone foradditional ethanol formation. Additionally or alternatively, all or aportion of the second residue may be directed to the first column inwhich acetic acid may be recovered in the first residue.

The ethanol mixture may be further processed in the second column torecover product ethanol. In some embodiments, it may be desirable tomaintain a concentration of water in the second column. Depending if awater separate is employed on the first distillate, and if so, the typeof water separator, the ethanol mixture may comprise less than 0.5 wt. %water. To control the water concentration, a by-pass line may be used tosplit the first distillate before or after the hydrolysis step, butpreferably before the water removal step. The split ratio may vary tocontrol the amount of water in the feed to the second column. In oneembodiment, the split ratio may range from 10:1 to 1:10, e.g., from 5:1to 1:5 or about 1:1. Other split ratios may be used when controlling thewater concentration. The distillate in the by-pass line is not separatedto remove water and may be combined or co-fed with the ethanol mixtureto the second column. The combined distillate and ethanol mixture mayhave a total water concentration of greater than 0.5 wt. %, e.g.,greater than 2 wt. % or greater than 5 wt. %. In terms of ranges, thetotal water concentration of the combined distillate and ethanol mixturemay be from 0.5 to 15 wt. %, e.g., from 2 to 12 wt. %, or from 5 to 10wt. %. The additional water for the second column may be recovered inthe second residue and/or in the ethanol side stream. As a result, itmay be desired depending on the intended application to separateremaining water from the ethanol side stream.

Exemplary ethanol recovery systems in accordance with embodiments of thepresent invention are shown in FIGS. 1 and 2. System 100 comprisesreaction zone 101 and separation zone 102. Hydrogen and acetic acid arefed to a vaporizer 110 via lines 104 and 105, respectively, to create avapor feed stream in line 111 that is directed to reactor 103. In oneembodiment, lines 104 and 105 may be combined and jointly fed to thevaporizer 110. The temperature of the vapor feed stream in line 111 ispreferably from 100° C. to 350° C., e.g., from 120° C. to 310° C. orfrom 150° C. to 300° C. Any feed that is not vaporized is removed fromvaporizer 110, as shown in FIG. 1, and may be recycled or discarded. Inaddition, although FIG. 1 shows line 111 being directed to the top ofreactor 103, line 111 may be directed to the side, upper portion, orbottom of reactor 103. Further modifications and additional componentsto reaction zone 101 and separation zone 102 are described below.

Reactor 103 contains the catalyst that is used in the hydrogenation ofthe carboxylic acid, preferably acetic acid. In one embodiment, one ormore guard beds (not shown) may be used upstream of the reactor,optionally upstream of vaporizer 110, to protect the catalyst frompoisons or undesirable impurities contained in the feed orreturn/recycle streams. Such guard beds may be employed in the vapor orliquid streams. Suitable guard bed materials may include, for example,carbon, silica, alumina, ceramic, or resins. In one aspect, the guardbed media is functionalized, e.g., silver functionalized, to trapparticular species such as sulfur or halogens. During the hydrogenationprocess, a crude ethanol product stream is withdrawn, preferablycontinuously, from reactor 103 via line 112.

The crude ethanol product stream in line 112 may be condensed and fed toa separator 106, which, in turn, provides a vapor stream 113 and aliquid stream 114. Suitable separators 106 include a flasher or aknockout pot. The separator 106 may operate at a temperature of from 20°C. to 250° C., e.g., from 30° C. to 225° C. or from 60° C. to 200° C.The pressure of separator 106 may be from 50 kPa to 2000 kPa, e.g., from75 kPa to 1500 kPa or from 100 kPa to 1000 kPa. Optionally, the crudeethanol product in line 112 may pass through one or more membranes toseparate hydrogen and/or other non-condensable gases.

The vapor stream 113 exiting separator 106 may comprise hydrogen andhydrocarbons, which may be purged and/or returned to reaction zone 101.As shown, vapor stream 113 is combined with the hydrogen feed 104 andco-fed to vaporizer 110. In some embodiments, the returned vapor stream113 may be compressed before being combined with hydrogen feed 104.

The liquid stream 114 from separator 106 is withdrawn and pumped to theside of distillation column 107. In one embodiment, the contents ofliquid stream 114 are substantially similar to the crude ethanol productobtained from the reactor in line 112, except that the composition hasbeen depleted of hydrogen, carbon dioxide, methane and/or ethane, whichare preferably removed by separator 106. Accordingly, liquid stream 114may also be referred to as a crude ethanol product. Exemplary componentsof liquid stream 114 are provided in Table 2. It should be understoodthat liquid stream 114 may contain other components, not listed, such ascomponents derived from the feed.

TABLE 2 COMPOSITION OF LIQUID STREAM 114 Conc. Conc. Conc. (wt. %) (wt.%) (wt. %) Ethanol 5 to 70    10 to 60 15 to 50 Acetic Acid <90    5 to80 15 to 70 Water 5 to 40    5 to 30 10 to 30 Ethyl Acetate <30  0.001to 20  1 to 12 Acetaldehyde <10 0.001 to 3 0.1 to 3  Acetal <5 0.001 to2 0.005 to 1    Acetone <5  0.0005 to 0.05 0.001 to 0.03  Other Esters<5 <0.005 <0.001 Other Ethers <5 <0.005 <0.001 Other Alcohols <5 <0.005<0.001

The “other esters” in Table 2 may include, but are not limited to, ethylpropionate, methyl acetate, isopropyl acetate, n-propyl acetate, n-butylacetate or mixtures thereof. The “other ethers” in Table 2 may include,but are not limited to, diethyl ether, methyl ethyl ether, isobutylethyl ether or mixtures thereof. The “other alcohols” in Table 2 mayinclude, but are not limited to, methanol, isopropanol, n-propanol,n-butanol or mixtures thereof. In one embodiment, the liquid stream 114,may comprise propanol, e.g., isopropanol and/or n-propanol, in an amountfrom 0.001 to 0.1 wt. %, from 0.001 to 0.05 wt. % or from 0.001 to 0.03wt. %. It should be understood that these other components may becarried through in any of the distillate or residue streams describedherein and will not be further described herein, unless indicatedotherwise.

Optionally, crude ethanol product in line 112 or in liquid stream 114may be further fed to an esterification reactor, hydrogenolysis reactor,or combination thereof. An esterification reactor may be used to consumeacetic acid present in the crude ethanol product to further reduce theamount of acetic acid to be removed. Hydrogenolysis may be used toconvert ethyl acetate in the crude ethanol product to ethanol inembodiments where a large amount of ethyl acetate is formed, althoughthe need for a hydrogenolysis unit is mitigated by the use of ahydrolysis unit as described herein.

In the embodiment shown in FIG. 1, line 114 is introduced in the middlepart of first column 107, e.g., second or third quarter. Depending onthe composition of the crude ethanol product in line 114 and theoperating conditions of first column 107, the first column 107 separatesthe crude ethanol product in line 114, preferably continuously, into afirst distillate in line 117 and a first residue in line 116. In oneembodiment, no entrainers are added to first column 107. The firstdistillate in line 117 comprises ethanol, other organics and water. Thefirst residue in line 116 comprises unreacted acetic acid, water, andother heavy components, if present. In some embodiments, especially withhigher conversions of acetic acid of at least 80%, or at least 90%, itmay be beneficial to remove a substantial portion of the water, e.g. atleast 35% to 90% of the water, from liquid stream 114, in the firstresidue along with substantially all the acetic acid.

When column 107 is operated under about 170 kPa, the temperature of theresidue exiting in line 116 preferably is from 90° C. to 130° C., e.g.,from 95° C. to 120° C. or from 100° C. to 115° C. The temperature of thedistillate exiting in line 117 preferably is from 60° C. to 90° C.,e.g., from 65° C. to 85° C. or from 70° C. to 80° C. In someembodiments, the pressure of first column 107 may range from 0.1 kPa to510 kPa, e.g., from 1 kPa to 475 kPa or from 1 kPa to 375 kPa.

The first distillate in line 117 comprises water, as discussed above, inaddition to ethanol and other organics, such as ethyl acetate and/orDEA. In terms of ranges, the concentration of water in the firstdistillate in line 117 preferably is from 4 wt. % to 38 wt. %, e.g.,from 7 wt. % to 32 wt. %, or from 7 to 25 wt. %. As shown in FIG. 1,prior to condensing the first distillate in line 117, first distillatein line 117 is fed to a hydrolysis unit 124 in which ethyl acetate andwater (preferably in excess) react to form ethanol and acetic acid. Thehydrolysis unit may comprise, for example, an ion exchange material orother material for catalyzing the hydrolysis reaction, as describedabove. After hydrolysis, the resulting ethanol mixture is directed to awater separator 118 for removal of water. Water separator 118 may be anadsorption unit, membrane, molecular sieves, extractive columndistillation, or a combination thereof.

In a preferred embodiment, water separator 118 is a pressure swingadsorption (PSA) unit. The PSA unit is optionally operated at atemperature from 30° C. to 160° C., e.g., from 80° C. to 140° C., and apressure of from 0.01 kPa to 550 kPa, e.g., from 1 kPa to 150 kPa. ThePSA unit may comprise two to five beds. Water separator 118 may removeat least 95% of the water from the first distillate in line 117, andmore preferably from 99% to 99.99% of the water from the firstdistillate, in a water stream 119. All or a portion of water stream 119may be returned to column 107, where it preferably is ultimatelyrecovered from column 107 in the first residue in line 116. Additionallyor alternatively, all or a portion of water stream 119 may be purged vialine 115. The remaining portion of first distillate 117 exits the waterseparator 118 as ethanol mixture stream 120. A portion of the firstdistillate in line 108 may be condensed and refluxed to first column107, as shown, for example, at a ratio of from 10:1 to 1:100, e.g., from2:1 to 1:50 or from 1:1 to 1:10. The reflux ratios may vary with thenumber of stages, feed locations, column efficiency and/or feedcomposition. Operating with a reflux ratio of greater than 3:1 may beless preferred because more energy may be required to operate the firstcolumn 107. Preferably, ethanol mixture stream 120 is not returned orrefluxed to first column 107. Optionally, a portion of the firstdistillate in line 108 is directed to the second column 109, as shown,to provide a limited amount of water, thereby facilitating residualethyl acetate separation from ethanol in the second column 109.

In another aspect, shown in FIG. 1, all or a portion of the water inwater stream 119 is fed to first column 107 at a point below where thefirst distillate in line 108 is refluxed to first column 107.

Exemplary components of the first distillate (before hydrolysis) andethanol mixture stream 120 (after hydrolysis and water removal) andfirst residue in line 116 are provided in Table 3 below. In a preferredembodiment, the first distillate initially comprises at least 0.5 wt. %ethyl acetate, e.g., at least 1 wt. % or at least 2 wt. % ethyl acetate,which may be hydrolyzed in the hydrolysis step. It should also beunderstood that these streams may also contain other components, notlisted, such as components derived from the feed.

TABLE 3 FIRST COLUMN WITH HYDROLYSIS UNIT AND PSA Conc. Conc. Conc. (wt.%) (wt. %) (wt. %) First Distillate (before hydrolysis) Ethanol 20 to 9530 to 95 40 to 95  Water <10 0.01 to 6   0.1 to 2   Acetic Acid <2 0.001to 0.5  0.01 to 0.2  Ethyl Acetate <60  1 to 55 5 to 55 Acetaldehyde <100.001 to 5    0.01 to 4    Acetal <0.1 <0.1 <0.05 Acetone <0.05 0.001 to0.03  0.01 to 0.025 Ethanol Mixture (after hydrolysis and water removal)Ethanol 20 to 95 30 to 95 40 to 95  Water <10 0.01 to 6   0.1 to 2  Acetic Acid <25 0.001 to 20   0.01 to 15   Ethyl Acetate <50 <45  <40    Acetaldehyde <10 0.001 to 5    0.01 to 4    Acetal <0.1 <0.1<0.05 Acetone <0.05 0.001 to 0.03  0.01 to 0.025 First Residue AceticAcid <90  1 to 50 2 to 35 Water  30 to 100 45 to 95 60 to 90  Ethanol <1<0.9 <0.3 

Some species, such as acetals, may decompose in first column 107 suchthat very low amounts, or even no detectable amounts, of acetals remainin the distillate or residue. In addition, an equilibrium reactionbetween acetic acid and ethanol or between ethyl acetate and water mayoccur in the crude ethanol product after it exits reactor 103. Dependingon the concentration of acetic acid in the crude ethanol product, thisequilibrium may be driven toward formation of ethyl acetate. Thisequilibrium may be regulated using the residence time and/or temperatureof crude ethanol product as well as in hydrolysis unit 124.

Depending on the amount of water and acetic acid contained in theresidue of first column 107, line 116 may be treated in one or more ofthe following processes. The following are exemplary processes forfurther treating first residue and it should be understood that any ofthe following may be used regardless of acetic acid concentration. Whenthe residue comprises a majority of acetic acid, e.g., greater than 70wt. %, the residue may be recycled to the reactor without any separationof the water. In one embodiment, the residue may be separated into anacetic acid stream and a water stream when the residue comprises amajority of acetic acid, e.g., greater than 50 wt. %. Acetic acid mayalso be recovered in some embodiments from first residue having a loweracetic acid concentration. The residue may be separated into the aceticacid and water streams by a distillation column or one or moremembranes. If a membrane or an array of membranes is employed toseparate the acetic acid from the water, the membrane or array ofmembranes may be selected from any suitable acid resistant membrane thatis capable of removing a permeate water stream. The resulting aceticacid stream optionally is returned to reactor 103. The resulting waterstream may be used as an extractive agent, for example to second column109 via line 121 as discussed below, or to hydrolyze an ester-containingstream in a hydrolysis unit.

In other embodiments, for example where first residue in line 116comprises less than 50 wt. % acetic acid, possible options include oneor more of: (i) returning a portion of the residue to reactor 103, (ii)neutralizing the acetic acid, (iii) reacting the acetic acid with analcohol, or (iv) disposing of the residue in a waste water treatmentfacility. It also may be possible to separate a residue comprising lessthan 50 wt. % acetic acid using a weak acid recovery (WAR) distillationcolumn to which a solvent (optionally acting as an azeotroping agent)may be added. Exemplary solvents that may be suitable for this purposeinclude ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate,vinyl acetate, diisopropyl ether, carbon disulfide, tetrahydrofuran,isopropanol, ethanol, and C₃-C₁₂ alkanes. When neutralizing the aceticacid, it is preferred that the residue in line 116 comprises less than10 wt. % acetic acid. Acetic acid may be neutralized with any suitablealkali or alkaline earth metal base, such as sodium hydroxide orpotassium hydroxide. When reacting acetic acid with an alcohol, it ispreferred that the residue comprises less than 50 wt. % acetic acid. Thealcohol may be any suitable alcohol, such as methanol, ethanol,propanol, butanol, or mixtures thereof. The reaction forms an ester thatmay be integrated with other systems, such as carbonylation productionor an ester production process. Preferably, the alcohol comprisesethanol and the resulting ester comprises ethyl acetate. Optionally, theresulting ester may be fed to the hydrogenation reactor.

In some embodiments, when the first residue comprises very minor amountsof acetic acid, e.g., less than 5 wt. %, the residue may be disposed ofto a waste water treatment facility without further processing. Theorganic content, e.g., acetic acid content, of the residue beneficiallymay be suitable to feed microorganisms used in the waste water treatmentfacility.

Reverting to FIG. 1, ethanol mixture stream 120 is introduced to asecond column 109, preferably in the top part of column 109, e.g., tophalf or top third. Second column 109 may be a tray column or packedcolumn. In one embodiment, second column 109 is a tray column havingfrom 5 to 70 trays, e.g., from 15 to 50 trays or from 20 to 45 trays. Asone example, when a 30 tray column is utilized in a column without waterextraction, ethanol mixture stream 120 is introduced at tray 2.

Optionally, the second column may be an extractive distillation column.Suitable extractive agents may include, for example, dimethylsulfoxide,glycerine, diethylene glycol, 1-naphthol, hydroquinone,N,N′-dimethylformamide, 1,4-butanediol; ethylene glycol-1,5-pentanediol;propylene glycol-tetraethylene glycol-polyethylene glycol;glycerine-propylene glycol-tetraethylene glycol-1,4-butanediol, ethylether, methyl formate, cyclohexane, N,N′-dimethyl-1,3-propanediamine,N,N′-dimethylethylenediamine, diethylene triamine, hexamethylene diamineand 1,3-diaminopentane, an alkylated thiopene, dodecane, tridecane,tetradecane, chlorinated paraffins, or a combination thereof. In anotheraspect, the extractive agent may comprise water. If the extraction agentcomprises water, the water may be obtained from an external source orfrom an internal return/recycle line from one or more of the othercolumns, such as the water stream 119. Generally, the extractive agentis fed above the entry point of ethanol mixture stream 120, as shown byoptional line 121. When extractive agents are used, a suitable recoverysystem, such as a further distillation column, may be used to remove theextractive agent and recycle the extractive agent if desired.

Second column 109 is operated to separate ethanol mixture stream 120 ora portion thereof into a second distillate in line 123, side stream 125comprising ethanol product, and a second residue in line 122. Seconddistillate in line 123 may comprise, for example, ethyl acetate andacetaldehyde, while second residue comprises acetic acid formed in thehydrolysis of the ethyl acetate. Second residue may be sent in whole orin part to the reactor for conversion to additional ethanol or sent tothe first column as discussed above. Side stream 125 comprises ethanoland, which optionally is a salable finished ethanol product. If water isadded to the second column 109, some water may be contained in secondresidue 122 and/or side stream 125, which may require an additionalwater removal step depending on the intended application for the ethanolproduct.

Although the temperature and pressure of second column 109 may vary,when at about 20 kPa to 70 kPa, the temperature of the second residueexiting in line 122 preferably is from 30° C. to 75° C., e.g., from 35°C. to 70° C. or from 40° C. to 65° C. The temperature of the seconddistillate exiting in line 123 preferably is from 20° C. to 55° C.,e.g., from 25° C. to 50° C. or from 30° C. to 45° C. The temperature ofthe side draw stream 125 preferably is from 30° C. to 75° C., e.g., from35° C. to 70° C. or from 40° C. to 65° C. Second column 109 may operateat a reduced pressure, near or at vacuum conditions, to further favorseparation of ethyl acetate and ethanol. In other embodiments, thepressure of second column 109 may range from 0.1 kPa to 510 kPa, e.g.,from 1 kPa to 475 kPa or from 1 kPa to 375 kPa. Exemplary distillate,side draw and residue compositions for second column 109 are provided inTable 4, below. It should be understood that the second distillate, sidestream and second residue may also contain other components, not listed,such as components in the feed.

TABLE 4 SECOND COLUMN Conc. Conc. Conc. (wt. %) (wt. %) (wt. %) SecondDistillate Ethyl Acetate  5 to 90 10 to 80  15 to 75 Acetaldehyde <60  1to 40   1 to 35 Ethanol <45 0.001 to 40   0.01 to 35 Water <20 0.01 to10  0.1 to 5 Side Stream Ethanol 50 to 99 60 to 99  70 to 99 Water <150.01 to 10  0.1 to 8 Ethyl Acetate 0.01 to 1   0.05 to 0.75  0.1 to 0.5Acetic Acid   <0.5 <0.01  0.001 to 0.01 Second Residue Ethanol 50 to 9960 to 90  65 to 85 Water <20 0.001 to 15   0.01 to 10 Ethyl Acetate  <10.001 to 2    0.001 to 0.5  Acetic Acid <15 <10    0.1 to 5

The weight ratio of ethanol in the side draw to ethanol in the seconddistillate preferably is at least 2:1, e.g., at least 5:1, at least 8:1,at least 10:1 or at least 15:1. The weight ratio of ethyl acetate in thesecond residue to ethyl acetate in the second distillate preferably isless than 0.4:1, e.g., less than 0.2:1 or less than 0.1:1.

Second distillate in line 123, which comprises ethyl acetate and/oracetaldehyde, preferably is refluxed as shown in FIG. 1, for example, ata reflux ratio of from 1:30 to 30:1, e.g., from 1:15 to 15:1 or from 1:5to 5:1. In one aspect, the second distillate in line 123 or a portionthereof may be returned reactor 103. For example, it may be advantageousto return a portion of second distillate 123 to reactor 103. The ethylacetate and/or acetaldehyde in the second distillate may be furtherreacted in hydrogenation reactor 103 or in a secondary reactor. Theoutflow from the secondary reactor may be fed to reactor 103 to produceadditional ethanol or to a distillation column, such as columns, 107,115, or 118, to recover additional ethanol.

In the embodiment shown in FIG. 1, the finished ethanol product producedby the process of the present invention may be taken from the sidestream in line 125. Advantageously, the finished ethanol product may berecovered using water separator and two columns according to the presentinvention. The finished ethanol product may be an industrial gradeethanol comprising from 75 to 96 wt. % ethanol, e.g., from 80 to 96 wt.% or from 85 to 96 wt. % ethanol, based on the total weight of theethanol product. Exemplary finished ethanol compositional ranges areprovided below in Table 5.

TABLE 5 FINISHED ETHANOL COMPOSITIONS Conc. Conc. Conc. Component (wt.%) (wt. %) (wt. %) Ethanol 75 to 96 80 to 96 85 to 96 Water <12 1 to 9 3to 8 Acetic Acid <1 <0.1 <0.01 Ethyl Acetate <2 <0.5 <0.05 Acetal <0.05<0.01 <0.005 Acetone <0.05 <0.01 <0.005 Isopropanol <0.5 <0.1 <0.05n-propanol <0.5 <0.1 <0.05

The finished ethanol composition of the present invention preferablycontains very low amounts, e.g., less than 0.5 wt. %, of other alcohols,such as methanol, butanol, isobutanol, isoamyl alcohol and other C₄-C₂₀alcohols. In one embodiment, the amount of isopropanol in the finishedethanol composition is from 80 to 1,000 wppm, e.g., from 95 to 1,000wppm, from 100 to 700 wppm, or from 150 to 500 wppm. In one embodiment,the finished ethanol composition is substantially free of acetaldehyde,optionally comprising less than 8 wppm acetaldehyde, e.g., less than 5wppm or less than 1 wppm.

In some embodiments, when further water separation is used, the ethanolproduct may be withdrawn as a stream from the water separation unit asdiscussed above. In such embodiments, the ethanol concentration of theethanol product may be higher than indicated in Table 5, and preferablyis greater than 97 wt. % ethanol, e.g., greater than 98 wt. % or greaterthan 99.5 wt. %. The ethanol product in this aspect preferably comprisesless than 3 wt. % water, e.g., less than 2 wt. % or less than 0.5 wt. %.

In another embodiment of the present invention, as shown in FIG. 2, thefirst distillate in line 117 from first column 107 passes to ahydrolysis unit 124 to convert ethyl acetate and/or DEA to ethanol andacetic acid or ethanol and acetaldehyde, respectively. The resultingstream is passed through a compressor 130 and is fed to a membrane 131.Membrane 131 preferably operates in the vapor phase. The water in thefirst distillate in line 117 permeates across the membrane 131 to form apermeate stream 132. Permeate stream 132 may comprise at least 80% ofthe water from the first distillate, and more preferably at least 90% ofthe water. In one embodiment, permeate stream 132 also comprises lessthan 10% of the ethanol from the first distillate, e.g., less than 5% ofthe ethanol. A portion of permeate stream 132 may be returned to column107, preferably below the feed point of the liquid stream 114. A portionof permeate stream 132 may be purged from the system, as shown by line133, to control the amount of water in column 107.

The portion of distillate that does not cross membrane 131 formsretentate stream 134, e.g., an ethanol mixture stream, and is fed tosecond column 109 as described above in FIG. 1. In one embodiment,retentate stream 134 comprises more water than shown in the ethanolmixture stream compositions provided in Table 3. For example, retentatestream 134 may comprise from 0 to 10 wt. % water, and more preferablyform 0 to 5 wt. % water. The additional water present in retentatestream 134 may be beneficial in separating ethyl acetate and ethanol insecond column 109. The additional water that is fed to second column 109preferably is removed with the second residue in line 122 and/or in theside stream 125 and may necessitate a secondary dewatering step, asdiscussed above, to provide an ethanol product having the desired waterconcentration.

Although one membrane is shown in FIG. 2, it should be understood that asuitable array of membranes may also be used.

In most embodiments of the present invention, it is desirable to removewater from the first distillate as shown in FIGS. 1 and 2. In FIG. 3,the first distillate in line 117, after passing through hydrolysis unit124, is split into a main line 140 and a hydrolyzed bypass line 144. Inone embodiment, the split ratio may range from 10:1 to 1:10, e.g., from5:1 to 1:5 or about 1:1. Main line 140 is fed to water separator 118 toproduce a water stream 142 and an ethanol mixture stream 143, whilehydrolyzed bypass line 144 is directed to second column 109. All or aportion of water stream 142 may be returned to first column 107 asdescribed above in FIGS. 1 and 2. A portion of first distillate in line117 may be condensed and refluxed to first column 107 via line 108,e.g., at a reflux ratio from 10:1 to 1:100, e.g., from 2:1 to 1:50 orfrom 1:1 to 1:10. An additional bypass line 141 may be taken from thereflux line 108 and fed directly to second column 109 along with ethanolmixture stream 143 and/or hydrolyzed bypass line 144. Flow controlvalves (not shown) may be used to control the split between the mainline 140, hydrolyzed bypass line 144 and additional bypass line 141 suchthat a desired water concentration is fed to the second column 109. Inone embodiment, a portion of bypass line 141 is refluxed to first column107, as shown. In another embodiment, bypass line 141 is not refluxed tofirst column 107 and a separate reflux line (not shown) may be provided.A portion of bypass line 141 may be condensed and separately fed tosecond column 109 with all or a portion of ethanol mixture stream 143.

The separation of the first distillate 117 into main line 140 and bypasslines 141 and 144 may be controlled based on the desired combinedconcentration of water of streams 141, 143, 144. In an embodiment,bypass line 141 contains a higher concentration of water than theethanol mixture stream 143 and hydrolyzed bypass stream 144. Thecombined water concentration of streams 141, 143, 144 optionally isgreater than 0.5 wt. %, e.g., greater than 2 wt. % or greater than 5 wt.%. In terms of ranges, the total water concentration of streams 141,143, 144 may be from 0.5 to 15 wt. %, e.g., from 2 to 12 wt. %, or from5 to 10 wt. %. The water content in bypass line 141 may be beneficialfor the separation of ethanol and ethyl acetate in distillation column109. In another embodiment, additional water may be added to column 109via line 121. Optionally, portions of the water in water stream 142 maybe added to column 109.

Each of the columns shown in FIGS. 1-3 may be selected from anydistillation column capable of performing the specified separationand/or purification step. Each column preferably comprises a tray columnhaving from 1 to 150 trays, e.g., from 10 to 100 trays, from 20 to 95trays or from 30 to 75 trays. The trays may be sieve trays, fixed valvetrays, movable valve trays, or any other suitable design known in theart. In other embodiments, a packed column may be used. For packedcolumns, structured packing or random packing may be employed. The traysor packing may be arranged in one continuous column or they may bearranged in two or more columns such that the vapor from the firstsection enters the second section while the liquid from the secondsection enters the first section, etc.

For convenience, the distillate and residue of the first column may alsobe referred to as the “first distillate” or “first residue.” Thedistillates or residues of the other columns may also be referred towith similar numeric modifiers (second, third, etc.) in order todistinguish them from one another, but such modifiers should not beconstrued as requiring any particular separation order. Similarly, themodifiers “first” and “second” when used to refer to distillationcolumns should be understood as being used to distinguish the reactorsrather than requiring that they be the first or second column,respectively, in the separation system. It is contemplated, for example,that a crude reaction product may be sent from a reactor or flash unitto an initial separation unite, e.g., distillation column, that forms acrude ethanol product that is then sent for processing in the first andsecond columns of the present invention.

The associated condensers and liquid separation vessels that may beemployed with each of the distillation columns may be of anyconventional design and are simplified in the figures. Heat may besupplied to the base of each column or to a circulating bottoms streamthrough a heat exchanger or reboiler. Other types of reboilers, such asinternal reboilers, may also be used. The heat that is provided to thereboilers may be derived from any heat generated during the process thatis integrated with the reboilers or from an external source such asanother heat generating chemical process or a boiler. Although onereactor and one flasher are shown in the figures, additional reactors,flashers, condensers, heating elements, and other components may be usedin various embodiments of the present invention. As will be recognizedby those skilled in the art, various condensers, pumps, compressors,reboilers, drums, valves, connectors, separation vessels, etc., normallyemployed in carrying out chemical processes may also be combined andemployed in the processes of the present invention.

The temperatures and pressures employed in the columns may vary. As apractical matter, pressures from 10 kPa to 3000 kPa will generally beemployed in these zones although in some embodiments subatmosphericpressures or superatmospheric pressures may be employed. Temperatureswithin the various zones will normally range between the boiling pointsof the composition removed as the distillate and the composition removedas the residue. As will be recognized by those skilled in the art, thetemperature at a given location in an operating distillation column isdependent on the composition of the material at that location and thepressure of column. In addition, feed rates may vary depending on thesize of the production process and, if described, may be genericallyreferred to in terms of feed weight ratios.

The finished ethanol composition produced by the embodiments of thepresent invention may be used in a variety of applications includingapplications as fuels, solvents, chemical feedstocks, pharmaceuticalproducts, cleansers, sanitizers, hydrogenation transport or consumption.In fuel applications, the finished ethanol composition may be blendedwith gasoline for motor vehicles such as automobiles, boats and smallpiston engine aircraft. In non-fuel applications, the finished ethanolcomposition may be used as a solvent for toiletry and cosmeticpreparations, detergents, disinfectants, coatings, inks, andpharmaceuticals. The finished ethanol composition may also be used as aprocessing solvent in manufacturing processes for medicinal products,food preparations, dyes, photochemicals and latex processing.

The finished ethanol composition may also be used as a chemicalfeedstock to make other chemicals such as vinegar, ethyl acrylate, ethylacetate, ethylene, glycol ethers, ethylamines, aldehydes, and higheralcohols, especially butanol. In the production of ethyl acetate, thefinished ethanol composition may be esterified with acetic acid. Inanother application, the finished ethanol composition may be dehydratedto produce ethylene. Any known dehydration catalyst can be employed todehydrate ethanol, such as those described in copending U.S. Pub. Nos.2010/0030002 and 2010/0030001, the entire contents and disclosures ofwhich are hereby incorporated by reference. A zeolite catalyst, forexample, may be employed as the dehydration catalyst. Preferably, thezeolite has a pore diameter of at least about 0.6 nm, and preferredzeolites include dehydration catalysts selected from the groupconsisting of mordenites, ZSM-5, a zeolite X and a zeolite Y. Zeolite Xis described, for example, in U.S. Pat. No. 2,882,244 and zeolite Y inU.S. Pat. No. 3,130,007, the entireties of which are hereby incorporatedherein by reference.

While the invention has been described in detail, modifications withinthe spirit and scope of the invention will be readily apparent to thoseof skill in the art. In addition, it should be understood that aspectsof the invention and portions of various embodiments and variousfeatures recited herein and/or in the appended claims may be combined orinterchanged either in whole or in part. In the foregoing descriptionsof the various embodiments, those embodiments which refer to anotherembodiment may be appropriately combined with one or more otherembodiments, as will be appreciated by one of skill in the art.Furthermore, those of ordinary skill in the art will appreciate that theforegoing description is by way of example only, and is not intended tolimit the invention.

We claim:
 1. A process for producing ethanol, the process comprising thesteps of: (a) hydrogenating acetic acid in a reactor in the presence ofa catalyst to form a crude ethanol product; (b) separating at least aportion of the crude ethanol product in a first distillation column toyield a first distillate comprising ethanol, at least 0.1 wt. % water,and ethyl acetate and a first residue comprising acetic acid; (c)hydrolyzing a portion of the ethyl acetate in the first distillate toform ethanol and acetic acid; and (d) separating at least a portion ofthe hydrolyzed first distillate in a second distillation column to yielda second distillate comprising ethyl acetate and a side streamcomprising from 10 wt. % to 99.5 wt. % ethanol, less than 1.0 wt. %ethyl acetate, and less than 1.0 wt. % acetic acid, and a second residuecomprising acetic acid; wherein the first distillate, prior tohydrolysis, has a water to ethyl acetate molar ratio of greater than3:1.
 2. The process of claim 1, wherein the ratio of ethanol in the sidestream to ethanol in the second residue is from 100:1 to 1:10.
 3. Theprocess of claim 1, further comprising the step of recycling at least aportion of the acetic acid from the second residue to the reactor. 4.The process of claim 1, further comprising the step of recycling atleast a portion of the acetic acid from the second residue to the firstdistillation column.
 5. The process of claim 1, further comprisingintroducing a water stream to the first distillate.
 6. The process ofclaim 1, wherein the hydrolyzing occurs in an ion exchange bed.
 7. Theprocess of claim 6, wherein the ion exchange bed is external from thefirst distillation column and between the first distillation column andthe second distillation column.
 8. The process of claim 1, wherein thefirst distillate initially comprises at least 0.5 wt. % ethyl acetate.9. The process of claim 1, wherein the first distillate initiallycomprises at least 1 wt. % ethyl acetate.
 10. The process of claim 1,wherein the first distillate initially comprises less than 2 wt. %acetic acid.
 11. The process of claim 1, wherein at least 95% of aceticacid fed to the first distillation column is separated into the firstresidue.
 12. The process of claim 1, wherein from 30 to 90% of the waterfed to the first distillation column is separated into the firstresidue.
 13. The process of claim 1, further comprising the step ofrecycling at least a portion of the ethyl acetate from the seconddistillate to the reactor.
 14. The process of claim 1, furthercomprising the step of recycling at least a portion of the ethyl acetatefrom the second distillate to the first distillation column.
 15. Theprocess of claim 1, further comprising the step of removing water fromat least a portion of the first distillate.
 16. The process of claim 15,wherein the first distillate comprises less than 10 wt. % water afterthe water removal step.
 17. The process of claim 15, wherein the wateris removed from the first distillate using an adsorption unit, membrane,extractive distillation column, molecular sieve, or a combinationthereof.
 18. The process of claim 15, wherein the water is removed fromthe first distillate using a pressure swing adsorption unit or a thermalswing adsorption unit.
 19. The process of claim 15, wherein a portion ofthe removed water is added to the second distillation column.
 20. Theprocess of claim 15, further comprising the step of adding water to thesecond distillation column under conditions effective to hydrolyze ethylacetate contained therein and form additional ethanol and acetic acid.21. The process of claim 1, wherein at least 10% of the ethanol fed tothe second column is recovered in the side stream.
 22. The process ofclaim 1, wherein the first distillation column is operated at a pressurefrom 6.9 to 68.9 kPaa.
 23. The process of claim 1, wherein acetic acidconversion in the reactor is at least 90%.
 24. The process of claim 1,wherein the first distillate is fed to the second column below the sidestream.
 25. A process for producing ethanol, the process comprising thesteps of: (a) hydrogenating acetic acid in a reactor in the presence ofa catalyst to form a crude ethanol product; (b) separating at least aportion of the crude ethanol product in a first distillation column toyield a first distillate comprising ethanol, at least 0.1 wt. % water,and ethyl acetate and a first residue comprising acetic acid; (c)hydrolyzing at least a portion of the ethyl acetate under conditionseffective to form additional ethanol and additional acetic acid; and (d)separating at least a portion of the first distillate in a seconddistillation column to yield a side stream comprising from 10 wt. % to99.5 wt. % ethanol, less than 1.0 wt. % ethyl acetate, and less than 1.0wt. % acetic acid, and a second residue comprising acetic acid, whereinthe second residue is returned to the reactor in step (a); and whereinthe first distillate, prior to hydrolysis, has a water to ethyl acetatemolar ratio of greater than 3:1.
 26. A process for producing ethanol,the process comprising the steps of: (a) hydrogenating acetic acid in areactor in the presence of a catalyst to form a crude ethanol product;(b) separating at least a portion of the crude ethanol product in afirst distillation column to yield a first distillate comprisingethanol, at least 0.1 wt. % water, ethyl acetate and a minor amount ofacetic acid and a first residue comprising acetic acid; (c) increasingthe amount of ethanol and the amount of acetic acid in the firstdistillate; and (d) separating at least a portion of the firstdistillate in a second distillation column to yield a second distillatecomprising ethyl acetate and a side stream comprising from 10 wt. % to99.5 wt. % ethanol, less than 1.0 wt. % ethyl acetate, and less than 1.0wt. % acetic acid, and a second residue comprising acetic acid; andwherein the first distillate in step (b) has a water to ethyl acetatemolar ratio of greater than 3:1.
 27. The process of claim 26, whereinwater is added to the first distillate under conditions effective tohydrolyze ethyl acetate contained therein and form ethanol and aceticacid.
 28. The process of claim 26, wherein the amount of acetic acid isincreased by at least 0.1%.
 29. The process of claim 26, wherein theamount of ethanol is increased by at least 0.1%.